As I wrote about last month, the knock on the PUE (Power Usage Effectiveness) metric from the Green Grid was its simplicity. There was simply too much going on that the metric didn't take into consideration for it to be a reliable way to evaluate, or even realistically compare, datacenter efficiency. Too many factors, from environmental cooling to on-site power generation, would skew the any potential comparison using the basic PUE number.

Yesterday the Green Grid released a report on a new model of PUE measurement that addresses many of the issues that limited the previous metric. "Recommendations for Measuring and Reporting Overall Data Center Efficiency - Version 1 - Measuring PUE at Dedicated Data Centers" was prepared by the Green Grid in conjunction with industry leaders in datacenter metrics and design: ASHRAE, the Uptime Institute, the US Department of Energy's Save Energy Now program, the US Environmental Protection Agency's Energy Star program, US Green Building Council, the Silicon Valley Leadership Group, and the 7x24 Exchange.

PUE is now broken down into 4 categories, 0 through 3, with 0 being a demand-based calculation that is most similar to the snapshot-like view of the original metric, while categories 1, 2, 3 are all consumption -based calculation based on actual usage measurements within the data center, with category 3 being the most detailed, consisting of 12 month total kWh measurements taken at the point of connection between individual IT devices and the electrical system.

In addition to more detailed types of usage measurements, the new model also is also weighted based on the type of source energy used to power the datacenter, giving a more accurate PUE representation when the datacenter makes use of alternative energy sources rather than just plugging into the normal electric grid. There is also a very clear definition of source energy; it represents the total amount of raw fuel required to operate the building, not just the power being fed into the IT components of the datacenter.

The complete document, including examples of the use of the new metric model, can be downloaded directly from the Green Grid website.

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